The present invention relates to an improved fireplace liner of the type in which air is heated in a heat exchange chamber and then circulated throughout the room. More specifically, the improvement comprises a thermally responsive closure device which permits entry of outside air into the heat exchange chamber for heating prior to subsequent passage out into the room.
Ordinary fireplace liners consist of a firebox connected to a flue and a heat exchange chamber located behind the firebox. The heat exchange chamber has air inlet openings at the base of the fireplace, generally near the floor, and outlet vents generally located above the fireplace. In operation, room air is brought into the lower openings, is heated by conduction within the chamber and is then passed through the outlet vents and back into the room. The heat exchange chamber is completely sealed from the firebox and flue to avoid mixing room air with the gaseous products of combustion.
Ordinary fireplace liners possess inherent disadvantages. For example, since the fire requires oxygen, the typical fireplace liner will function properly only when the room or house is improperly sealed from the outside environment. As the fire burns, make-up air is drawn in from the outside, generally through cracks around the doors and windows. The passage of air from the outside through these cracks creates localized cold air drafts which can be both annoying and unhealthy to room occupants. Additionally, if a house is too tightly sealed, the fire burns incompletely, resulting in partially burned logs. Furthermore, if there is no adequate supply of fresh air because of the tight seal, the removal of oxygen from the room often results in a feeling of drowsiness by occupants of the room.
In those fireplace liners which have means for bringing outside air into the heat exchange chamber, there exist various types of closure devices which block the access to the outside when the fireplace is not in use. These devices are activated either manually or electrically. Thus, when a fire is started in a fireplace, one must wait until it is sufficiently hot and then must either manually open the access to the outside or activate an electrical switch which then opens the closure device. Quite frequently, one forgets to open the closure device, and in such an instance the fireplace liner does not even operate as an ordinary liner. Rather, the fireplace functions strictly in the conventional sense. That is, there is neither recirculation of room air, nor circulation of outside fresh air within the room.
The present invention solves the inherent problems of ordinary fireplace liners as well as the specific problems existing in those fireplace liners which utilize outside air. The invention provides for automatic opening of the access to the outside when the fire within the firebox reaches a predetermined temperature. When the fireplace cools, the closure device returns to its normally closed position, thus blocking the entrance of outside cold air. U.S. Pat. No. 3,134,377 discloses a thermally responsive vent, located within a flue damper, which automatically closes and blocks access to the flue when the fire within the fireplace has gone out.